Plugin Documentation is now hosted on the plugin's github account and accessed via this link
Plugin Editors will need to will need to use the “Edit this page” button or install and use the asciidoc / antora system and github pull requests to edit Plugin Pages. Please see Authoring Plugins for information about implementing asciidoc/antora and editing of plugin documentation.
The reasons we have converted the Developer and Plugin Documentation to asciidoc/antora is found here Manage Docs as Code and Why AsciiDoc/Antora? Use Overview- Vimeo
The older Plugin Package Installer (which still works) has been replaced by the Plugin Manager (PIM) which is integrated into OpenCPN. Eventually the Plugin Package Installer system will become obsolete and deprecated.